This invention relates to unloading and emptying means for bulk material in store houses and ship cargo holds. By bulk material is meant granular material with a capacity to slide and of different origin and particle size, such as grain, salt, fertilizers and the like.
There is known equipment for this purpose using scraper conveyors attacking the bulk material from above and moving it in the longitudinal direction of the room or hull. Due to the fact that the width of attack will be limited to the width of the individual scrapers, it will also be necessary to move the scraper conveyor transverse to the work direction, i.e. back and forth in the transverse direction of the room so that the total surface area of the store room will be covered. Furthermore, it will be necessary to be able to move the scraper conveyor vertically, so that it can be lowered at the same rate as the surface of the bulk material, as this is sinking due to the unloading. Scraper conveyors of this type are generally known, for instance from French Pat. No. 1,343,751.
As a result of the work of the scraper conveyor the bulk material will be moved in the longitudinal direction of the room and collects near one of the walls of the room, from where it can be transported out of the room by suitable elevator means which extend to the bottom of the floor.
When the elevator means is in the form of a stationary elevator, for instance a bucket elevator driven by endless chains, with the buckets mounted on the chains, there must also be provided means for transverse transportation of the bulk material, i.e. in a direction crossing the longitudinal direction, to the stationary elevator means.
Such transverse transportation may also conveniently be provided by means of a scraper conveyor, which either can be mounted near or at the bottom floor or on the surface of the bulk material. In the last mentioned case this transverse scraper conveyor must also be able to move in the vertical direction to progress together with the surface of the bulk material when it is gradually decreasing or sinking down during unloading.
Equipment of the last mentioned type is known and described in German Specification DOS No. 2,800,226, published July 18, 1978, but at that time not taken into practical use. Equipment of the first mentioned type is, however, also known, and since 1973 has been in practical use for transport of fertilizers in bulk ships. The solution using a scraper conveyor moving near the bottom of the cargo hold was chosen because one wished to use the transverse conveyor in combination with the lifting gear of the elevator, a bucket elevator which was extended completely down to the bottom of the hull, and thereby obtain a simpler and less costly construction. The choice between surface scraping or scraping at the bottom will also to a certain extent depend on the type of bulk material which is to be transported and how easily it slides.
The known unloading gear of this type utilizes scraper conveyors mounted on elongated guide beams which partly or completely cross the cargo hold. Furthermore, these beams are suspended in and mounted to be vertically movable by means of wires or chains hanging freely down from the roof or ceiling. The transmission of electrical current to the drive means situated on the scraper conveyors must also be done with long movable cables. This requires much space and causes great problems, not only for the unloading functions, but also when the hull must be loaded again with bulk material.